I. Field of the Invention: The invention concerns a manometer with a pressure-measuring cell, in particular, a piezoresistive pressure-measuring cell having a protective layer of glass except in the contact region where the glass protective layer is removed or omitted and the region is sealed with a glass-free casting compound.
II. Discussion of the Prior Art: Piezoresistive pressure-measuring cells and/or sensor have been disclosed, for example in DE-OS 33 44 799. As a rule, they consist of a capsule-shaped pressure-measuring cell with a piezoresistive resistance provided on a measuring membrane, with the measuring membrane being firmly joined, via a circular holder, with a base plate located thereunder. The pressure-measuring cell constructed as a silicon cell is cohesively built on a support. These supports are most often so-called glass feedthroughs through which the separate lines leading to connection points on the measuring membrane pass and that are soldered to the connection points of the pressure-measuring cell. In this manner, the measuring cell can only be used in dry air or in an insulated liquid. Therefore, the measurement cells are generally built into a steel housing in which they are isolated from the electrically-conducting, humid or aggressive pressure medium with a medium-isolating membrane.
For the further transmission of pressure, oil is poured into the thusly formed measuring membrane inner space accommodating the pressure-measuring cell. However, in this type of encapsulated, oil-filled design, the connecting wires that are usually manufactured as gold or aluminum wires are strongly stressed by vibration and pressure shocks, so that the wires are often broken by fatigue fractures.
Therefore, proposed in DE 35 00 613 Al is a method of connecting to the pressure-measuring cell using the so-called TAB technique (Tape Automated Bonding), where a thin sealing lip is made about the connecting points on the pressure-measuring cell, between the section of plastic foil material with the connecting wires and the top side of the measuring membrane, sometimes about an individual conductor or about several conductors in common. In this manner, the pressure-measuring cell could basically be employed directly in wet and conducting media without a transmission membrane and a corresponding transmission membrane housing. This method, however, because of the great technical problems when mounting the thin sealing elements, has basically demonstrated itself to be unfavorable.
To eliminate use of a steel housing with a transmission membrane for protecting the pressure-measuring cell against the possibly aggressive pressure medium to be measured, for reasons of cost, it has already been tried to protect the measuring cell contacts in a less expensive manner so that they can also be used in uninsulated media.
Additionally, measuring cells can today be protected with a gel, a highly viscous liquid on a silicone base, for example in a coating and/or vaporizing process. Typically, such materials are called vaporization materials capable of being vaporized at low temperature, typically below 700.degree., in order to prevent injury to the connections. Such connections frequently consist of aluminum. This solution is suitable for use in humid or partially wet media, but only in the case of relatively low pressures and, in particular, where there are no abrupt changes in pressure. In the case of abrupt pressure changes, the gel can be thrown out of position. Also, under pressure and temperature, the gel can hold back the moisture only in limited fashion and, in any case, not continuously.